The present invention relates broadly to optical communications systems, and in particular to a low power frequency modulated hybrid fiber optic data transmission system.
In the testing of many electrical devices or systems which are required to transmit electrical signals or intelligence, a high degree of radio frequency interference security is necessary to insure accurate signal reproduction during monitoring. Screen rooms or anechoic chambers which have been utilized in the prior art for conducting sensitive RFI measurements, function on the principle of providing a high attenuation of spurious electromagnetic interference from within and without the test environment. However, such a shielded enclosure sometimes requires the transmission of data or electrical signals from the equipment within the shielded room to monitoring or control equipment outside the protected environment. These transmission links are a frequent source of cross-coupling for spurious electro-magnetic interference. In other words, RFI signals external to the chamber may enter the chamber, and the controlled r-f environment inside the chamber may be altered by absorption and reflection properties of hard wire cables.
In the prior art, when a transmission line has been employed to couple signals from within to without a shielded room, the elimination of spurious or undesired signals has been partially accomplished by the use of filters in the signal transmission line. This is not entirely satisfactory, however, because filters are basically bilateral devices which will conduct in either direction and will not prevent undesired signals from being passed if they are within the frequency pass band of the filter.
In addition, a specific problem which has been encountered is the testing of weapon systems that are susceptible to radio frequency jamming. The testing of such systems requires that the system be situated in a radio frequency controlled environment with no metallic wire or similar such paths linking the outside monitoring area with the interior of the chamber. The present invention utilizes a fiberglass transmission medium to link the monitored points of the weapon system within the chamber to the external monitoring station.